Liquid unloading method and apparatus



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Aug. 22, 1967 K|Y05H1 SHlBATA ET AL 3,336,915() LIQUID UNLoADING METHOD AND APPARATUS Filed July 3l, 1963 2 Sheets-Sheet l N A N N \1-\ J w W A v @l N l l fn l N N, d O\ E A E A! Q LQ u a l lo m E N MQ QQ D Q Q En N w m w 5 89x59 y 9 `\3\1 INVENTORS YasH/ .SW/@47,4 BYASE/VA/as u/(E Susann MAA/fw ATTORNEYS ug. 22, 1967 K|Y05H| S|||BATA ET AL 3,336,930

LIQUID UNLOADING METHOD AND APP/:xmmsv Filed July 51, 1963 2 sheets-sheet 2 INVENTORS AO rasy/ .SW/5,4 7u:

EN Nasa/(6 Sas U04 ATTORNEYS United States Patent O 3,336,930 LIQUID UNLOADING METHD AND APPARATUS Kiyoshi Shibata, 886 4-chome, Saginomiya, Nakano-ku, Tokyo-to, and Sennosuke Susuda, 433 Seya-machi, Ichikawa-shi, Chiba Prefecture, Japan Filed .luly 31, 1963, Ser. No. 298,869 Claims priority, application Japan, Aug. 2, 1962, 37/ 32,237 4 Claims. (Cl. 137-13) The present invention relates to a system for the removal of liquid stored in containers or the like, and in particular to an improved system for the removal of liquid cargo or ballast from a ship.

In liquid removal systems and in particular systems utilized for the removal of liquid from cargo carrying ships, to which embodiment the drawings of the present application are directed, it has been customary to employ more than one type of pump. In the usual two pump system a centrifugal pump and a piston pump are employed. The centrifugal pump is utilized to remove the bulk of the liquid because such pumps are easier to maintain, have less parts subject to wear etc., which reduce the cost of operating such a pump.

However, it is well known that centrifugal pumps can operate efficiently only if the density of the fluid being removed thereby is above a certain predetermined point. Thus, if the density of the liquid falls below the critical point because, for example, air mixes in with the liquid, the etciency of the pump will be lowered or the pump will become inoperative, according to the construction of the pump and the density of the liuid. In such liquid removal systems as the liquid level in the storage tank being emptied falls below the critical point air begins to be sucked into the centrifugal pump along with the liquid to the detriment of the etiicient operation of the pump. In the systems heretofore employed when the liquid level reached the critical point, secondary piston pumps were cut in to complete the removal of the remainder of the liquid in the tank. Piston pumps are utilized in this manner `because they are not adversely affected by a mixture of air with the liquid being removed.

It can be understood that a system for obviating the necessity of employing a multiple type pump system, as described above, would be a significant advance in the art because the number and complexity of the pumps and associated piping would be considerably reduced thereby lowering the cost of the system.

It is, therefore, an object of the present invention to provide an improved system for the removal of liquid from a storage means.

It is another object of this invention to provide a system for the complete removal of liquids from storage means utilizing only one type of pump.

It is still another object of the present invention to provide a system for the ecient removal of liquids from a storage means by employing centrifuga-l pumps alone.

For other objects and a better understanding of this invention, reference may be had to the detailed description herein below, taken in connection with the accompanying drawings.

The present invention provides a relatively small secondary tank in fluid connection with a main storage tank containing the liquid to be removed therefrom. The secondary tank in turn, is connected by suitable valves and piping to a pump such as a centrifugal pump which, when actuated Serves to remove liquid from within the secondary tank. The pressure in the secondary tank is maintained below that of the main tank, with which it is fluidly connected. The pressure differential induces the liquid in the main tank to dow into the secondary tank as the pump sucks the liquid from the secondary tank.

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When the level of the main tank is lowered to a critical point air begins to be pulled into the secondary tank along with the liquid. The air pulled into the secondary tank serves to increase the pressure of the secondary tank and lower the liquid level in the secondary tank. If the liquid level in the secondary tank were to fall too far, the operation of the centrifugal pump would become impaired, as explained above. To reduce the pressure to the desired degree a compressor, connected, to the secondary tank, is actuated and air is removed from the secondary tank. The liquid level within the secondary tank is then returned to the height desired, as the pressure is reduced.

Thus, it can be understood that a predetermined height of liquid Within the secondary tank may be maintained. The centrifugal pump may therefore continuously remove liquid, and liquid only, from the secondary tank. Since the secondary tank is fed by the main tank, it follows that the liquid stored within the main tank is also removed. Thus, the liquid in the main tank may be cornpletely removed 'without danger of air being sucked into' the pump.

For a better understanding of the invention, its operating advantages and specilic objects obtained by its use, reference may be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

In the drawings:

FIG. l is a schematic representation of a plan View of a portion of a liquid cargo carrying ship and the pumping system associated therewith.

FIG. 2 is a sectional view of the portion of the ship shown in FIG. 1.

Referring now more in detail to the drawings, wherein similar reference numerals identify corresponding parts, 10 represents a liquid cargo pumping system for a ship substantially as shown.

A main liquid cargo storage tank 12 is divided into a plurality of compartments by bulkheads 14. A secondary liquid tank 16 is formed adjacent main tank 12. The secondary tank 16 includes air tight bulkheads 18. A pump room 20 is conveniently positioned adjacent the secondary tank and an engine room 22 is set out next to the pump room, as best seen in FIG. 1. A pair of fuel oil bunkers 24 are positioned one on each side of the pump and engine room and adjacent coiferdams 2S. The cofferdams are situated such that one side of each is adjacent the main tank and one side is adjacent the secondary tank. The above described compartments are enclosed by walls 26, flooring 28 and by deck 30. Bulkheads 32 serve to separate the oil bunkers from the pump and engine rooms and bulkhead 34 partitions the pump and the engine room.

Having described the physical structure which encloses the pumping system, the following description will set forth the physical structure and general placement of the elements of the pumping system. Thus, pumps 36, which in the embodiment disclosed are centrifugal pumps, are suitably positioned within pump room 20. 'Ihe pumps 36 are driven by suitable prime movers 38 situated in engine room 22. Pumps 36, prime movers 38 and their interconnections are well known in the art and their specific structure will not be set forth in this application. Suction pipes 40 provide fluid connection between pumps 36 and secondary liquid tank 16 through suitable valves 42. A bell mouth iixture 44 is connected to the end of each suction pipe 40 and these fixtures are positioned on the bottom of the secondary liquid tank and provide for the passage of the liquid therethrough into the suction pipes. Main liquid cargo pipes 46 pass through main tank 12 and through valves 48 into the secondary liquid tank. Bell mouth fixtures 50 are xed on the bottom of the D main tank and provide a fluid connection to the main liquid cargo pipes through pipes 52 and valves S4.

Discharge pipes 56 connected to pumps 36 pass out of the tanker to liquid receiving apparatus 57 through threeway valves 58. Secondary discharge pipes 60 lead from three-way valves 58 through valves 62 into secondary liquid tank 16.

A compressed air tank 64 positioned Within engine room 22 supplies air through compressor conduit 66 to ejector 68. Conduit 70 connects ejector 68 to the ambient atmosphere. Secondary tank conduit 72 provides a tiuid connection between secondary tank 16 and ejector 63, through valve 74. A suitable compressor 76 provides for the maintenance of the necessary pressure of the air in compressed air tank 64. Ejector 68 and its associated elements provide for the withdrawal of air from the secondary tank for reasons to 4be explained hereinbelow.

Turning now to the operation of the novel system comprising the present invention, when the operator wishes to unload the liquid cargo from the main tank 12 he begins by opening valves 48 and 54 in the main tank and valves 42 connecting the pump with the secondary tank 16. In addition, three-way valve 58 is adjusted to provide a direct connection through discharge pipe 56 to liquid receiving apparatus 57, positioned externally of the tanker. At this point, secondary discharge pipes 60 are not in liquid connection with discharge pipes 56. Pumps 36, driven by prime movers 38 are actuated and the liquid Within the secondary tank is sucked therefrom, by the action of the pumps, through the suction pipes and out to the receiving apparatus. As the liquid is removed from the secondary tank the level of the liquid within said tank tends to lower to a point which is lower than the level of the liquid within the main tank 12, both tanks being full at the start. However, since valve 74 at this point in the operation is closed, the secondary tank is air tight and as the liquid level drops in the secondary tank a negative pressure, that is a pressure below the level of atmospheric pressure, is produced. The negative pressure within the secondary tank acts as a suction to draw the liquid from within the main tank 12 into the secondary tank through the appropriate pipes and valves. Thus, a continuous ow from the main tank 12 through secondary tank 16, suction pipes 40, pumps 36, discharge pipes 56, and into receiving apparatus 57 is maintained while the pumps 36 are operating.

It should be noted that the main tanks 12 are not air tight and have access to the atmosphere. Thus, there is at all times a pressure equal to atmospheric pressure supplied to the liquid Within the main tanks. Since the pressure in the secondary tank is maintained at a predetermined degree below atmospheric pressure a pressure differential is produced which forces the liquid through the system, as described herein. Thus, regardless of how low the level of the liquid in the main tank drops, even though it is below the level of the liquid within the secondary tank, so long as the pressure within the secondary tank is maintained at a low enough level the liquid will be continuously sucked from the main tank into the secondary tank.

As the liquid level in the main tank approaches the bottom of the tank and a predetermined critical point is reached, air becomes intermingled with the liquid being sucked into the secondary tank. When this happens the air pulled along with the liquid into the secondary tank rises to the top of that tank to increase the pressure within the tank. If this were allowed to continue the pressure would increase to a point where the liquid within the main tank would not be pulled into the secondary tank and the liquid level in the secondary tank would drop to a point where the pumps 36 would begin to suck in the air thereby undermining the operation of the pump. When this occurs and the level of the liquid within the secondary tank reaches a predetermined point, valve '72 is opened and ejector 68 goes into operation to thereby remove air from the secondary tank to bring the pressure and consequently the liquid level back to the normal operating point. The ejector may be actuated by any suita-ble automatic or manual means.

However, in the event that the air sucked into the secondary tank is so great that the ejector cannot at iirst remove a suiiicient amount of air from the secondary tank fast enough to keep the level of the liquid in the secondary tank from dropping below the predetermined critical level, three-way valve 58 is adjusted to either automatically or manually cut in secondary discharge pipes 66. Valves 62 are opened and a portion of the liquid being pumped from the secondary tank is returned to that tank through the three-way valves, pipes 6i) and valves 62. The liquid thus returned helps to restore the level of the liquid within the secondary tank to a height sucient to prevent the pump from sticking in air along with the liquid from the secondary tank.

From the foregoing, it can be understood, that the main tank can be completely emptied of its liquid cargo by employing only one type of pump (centrifugal). Thus, it is not necessary to interrupt one set of pumps and bring another set of pumps into operation. Because the secondary tank has very small dimensions the amount of liquid remaining therein, after the main tank has been emptied and the level of the secondary tank has been reduced to the point where the centrifugal pump becomes inoperative, is so little relative to the amount of the total liquid cargo as to be unimportant. The small `amount remaining may be left in the secondary tank, or if desired may be removed very quickly by any suitable means. Thus, the secondary tank forms a means for maintaining the centrifugal pump operative until substantially all of the liquid cargo is removed from the main tank and until the secondary tank contains an amount of liquid which is so small as to be negligible in comparison with the liquid removed from the main tank through the secondary tank.

It should be noted that the secondary tank may be divided into a plurality of compartments to thereby provide for more than one type of fluid to be separately removed from its corresponding main tank. In addition, the main and secondary tanks may be directly connected through valves positioned within the dividing air tight bulkhead in lieu of the main liquid cargo pipes running through the ymain tank. Further, i-t should be noted that the present system may be utilized with tanks containing other than cargo for example, ballast tanks aboard a ship.

It can be appreciated therefore, that by reducing the dual pump system to a single type pum-p system, the complex problem, encountered in dual pump systems, of timing the changeover from the centrifugal pump to the piston 4pump is obviated, whether the changeover be automatic, requiring additional controls, or manual. Furthermore, the .reduction in the number of pumps and in the amount of pipeline, and the simplified arrangement of the pipes effects a considerable savings in the cost of designing and manufacturing such a system. ln addition, since the amount and complexity of the required equipment is reduced, handling and maintenance of the system is also reduced, thereby further reducing the cost of the system.

While various embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it should be understood that the invention may be embodied otherwise without departing from such principles.

We have described what we believe to be the best embodiments of our invention. We do not wish, however, to be coniiined to the embodiments shown, but what we desire to cover by Letters Patent is set forth in the following claims.

What is claimed is:

1. A liquid removal system, comprising a main storage container of relatively large volume for storing a liquid, said main container communicating with the outer atmos- -phere so as to be at atmospheric pressure, a secondary huid-tight container of a relatively small volume which is only a negligible fraction of the volume of said main container, means for providing a fluid connection between said main storage container and said secondary container, pump means exclusively of the centrifugal type in fluid connection with said secondary container for removing substantially all of the liquid from said main storage container through said secondary container, means for reducing the pressure in said second-ary container to an extent which will maintain therein suicient liqiud for proper operation of said pump means, and Valve means for returning a portion of liquid -pumped through said secondary container back to said secondary container.

2. A system as in claim 1, wherein said pressure reducing means includes an ejector. Y

3. A system for removing liquid from a ships storage container, comprising a lirst container at atmospheric pressure positioned aboard the ship to store a liquid, a second air tight container of a relatively small volume which is a negligible fraction of the volume of said first container, pipe means connecting said rst container to said second container for directing to the latter substantially Iall of the liquid in said first container, at least one centrifugal pump, a suction pipe connecting said centrifugal pump with said second container, a discharge pipe -uidly connecting said centrifugal pump with a liquid receiving apparatus, a three-way valve positioned in said discharge pipe, a secondary discharge pipe iluidly connecting said three-way valve with said second liquid container whereby said three-way valve may be actuated to allow a portion of the liquid being removed from said second container by said centrifugal pump to be returned to said second container, and means for reducing the pressure in said second liquid container to thereby allow the liquid in said rst container to be sucked into said second container when said centrifugal pump is operating and to maintain in ysaid second container sufficient liquid for proper operation of said centrifugal pump.

4. A method of unloading liquid cargo, comprising the steps of directing substantially all liquid in a main storage container into a second container large enough to maintain a sufficient amount of liquid for proper oper-ation of a centrifugal pump by maintaining the pressure in the second container below that of the main container, centrifugally pumping liquid from said second container so e References Cited UNITED STATES PATENTS 1,202,050 10/ 1916 Gamble 137-565 1,482,376 2/1924 Anderson 10S-113 2,404,869 7/ 1946 Sorrentino 137-5 65 3,010,470 11/1961 Clymer 137-147 M. CARY NELSON, Primary Examiner.

W. R. CLINE, Assistant Examiner. 

1. A LIQUID REMOVAL SYSTEM, COMPRISING A MAIN STORAGE CONTAINER OF RELATIVELY LARGE VOLUME FOR STORING A LIQUID, SAID MAIN CONTAINER COMMUNICATING WITH THE OUTER ATMOSPHERE SO AS TO BE ATMOSPHERIC PRESSURE, A SECONDARY FLUID-TIGHT CONTAINER OF A RELATIVELY SMALL VOLUME WHICH IS ONLY A NEGLIGIBLE FRACTION OF THE VOLUME OF SAID MAIN CONTAINER, MEANS FOR PROVIDING A FLUID CONNECTION BETWEEN SAID MAIN STORAGE CONTAINER AND SAID SECONDARY CONTAINER, PUMP MEANS EXCLUSIVELY OF THE CENTRIFUGAL TYPE IN FLUID CONNECTION WITH SAID SECONDARY CONTAINER FOR REMOVING SUBSTANTIALLY ALL OF THE LIQUID FROM SAID MAIN STORAGE CONTAINER THROUGH SAID SECONDARY CONTAINER, MEANS FOR REDUCING THE PRESSURE IN SAID SECONDARY CONTAINER TO AN EXTENT WHICH WILL MAINTAIN THEREIN SUFFICIENT LIQUID FOR PROPER OPERATION OF SAID PUMP MEANS, AND VALVE MEANS FOR RETURNING A PORTION OF LIQUID PUMPED THROUGH SAID SECONDARY CONTAINER BACK TO SAID SECONDARY CONTAINER. 